Hi
I'm AnnaThomas and I'd happily help you with your question. In this Forum, we are Microsoft consumers just like yourself.
It seems that you are not alone in experiencing this issue with the searchable drop-down list feature in Office 365. It appears that the feature is being gradually deployed and could be pulled out at any time.
This means that some users may have access to the feature while others do not. You can leave a feedback about this
https://feedbackportal.microsoft.com/feedback
Learn more: https://answers.microsoft.com/thread/e0133d2b-9916-4d2e-8494-1fcffbb1653f
I hope this helps ;-), let me know if this is contrary to what you need, I would still be helpful to answer more of your questions.
Best Regards,
AnnaThomas
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